'thermostat' for anesthesia

A study reports on an automated anesthesia system that can maintain a precise level of unconsciousness, much as a thermostat adjusts heating and cooling to maintain a steady temperature. Anesthesiologists seeking to ensure that patients will not regain consciousness during surgery often administer anesthetic doses beyond what are needed to maintain an adequate level of unconsciousness, a habit which can increase the incidence of post-operative cognitive disorders. The goal of a closed-loop anesthesia delivery (CLAD) system is to maintain a precisely set level of unconsciousness in a patient automatically, by continuously monitoring brain waves and adjusting the dosage of anesthetic medications accordingly. Although such a system would be valuable for intraoperative patient management and help avoid the need for heavy dosing, none has yet been approved by the Food and Drug Administration, in part because of a lack of testing in appropriate animal models. Emery N. Brown and colleagues designed a system that was able to keep rhesus macaques at different preset levels of unconsciousness for total of 18 hours and 45 minutes across nine experiments of about two hours each. The neural data acquisition system continuously recorded the primates' local field potentials, which were then computationally compared to a desired marker of unconsciousness based on cortical spike rates. When the marker of unconsciousness began to depart from the prescribed target level, the infusion rate of the anesthetic drug, propofol, was automatically adjusted. The authors plan additional studies to explore other markers of unconsciousness and to autonomously handle anesthesia induction and emergence as well as maintenance. The eventual goal is a CLAD system that can be used on human patients in the operating room as well as in the intensive care unit, according to the authors.